The present invention relates to an espresso coffee machine.
On espresso coffee machines, ground coffee is placed inside a cup-shaped filter housed removably inside a percolator cup presenting at least one outflow conduit at the bottom, and connectable at the top, by means of a bayonet joint, to a tubular body or support surrounding the outlet of a hot-water supply device normally consisting of a boiler.
On known machines of the aforementioned type, to fit the cup inside the tubular support and tighten the bayonet joint, the cup is moved axially in relation to the tubular support, and the free edge of the cup is connected in fluidtight manner to a face seal fitted to the tubular support and surrounding the outlet of the hot-water supply device. Fluidtight connection of the cup to the tubular support provides for defining a mixing chamber divided by the filter into two parts, one communicating solely with the outlet of the hot-water supply device, and the other communicating solely with the bottom outflow conduit, so that the pressurized hot water from the supply device is forced to flow through the filter and the ground coffee inside it to reach the bottom outlet conduit.
Known machines of the aforementioned type present several functional and operating drawbacks. In particular, sealing of the mixing chamber is achieved by tightening the bayonet joint, which not only requires practice and a certain amount of effort on the part of the user, but also involves a varying angular position of the cup in relation to the tubular support, depending on the elastic reaction of the seal. In other words, no one precise position exists in which to fit the cup to the tubular support, and sealing of the mixing chamber is only ensured by exerting considerable effort which may even result in the cup jamming inside the support. Moreover, known machines of the above type only operate particularly well using loose ground coffee as opposed to cakes which differ in shape. As such, a machine designed to receive a certain type of cake may prove absolutely incapable of sealing the mixing chamber, and hence producing good quality espresso coffee, when a different type of cake is used.